A Fresnel lens consists of a central lenticular part generally encircled with structures forming concentric rings (spherical lens) or having linear shapes (cylindrical lens).
The optical quality of a Fresnel lens depends inter alia on the shape of the Fresnel zones, on the surface finish, on the material and on the vertical walls separating two consecutive zones.
A Fresnel lens may have, relative to a conventional convergent lens, a smaller thickness and therefore, advantageously, a higher optical transmission coefficient for the same interception area.
Various process are known for manufacturing Fresnel lenses.
It is, for example, known from JP 062 341 56 to manufacture Fresnel lenses by hot stamping, in which a tool is heated and pressed into a thermoformable material so as to form the Fresnel zones of said lens.
Fresnel lenses may also be manufactured by molding. A method for manufacturing a mold is described in US 2006/0234607.
Hot-stamping or molding manufacturing methods may have the drawbacks of limiting the profile of the Fresnel lenses thus obtained to the shape of the stamp or mold used and of restricting the materials that can be used to thermoformable materials.
JP 2009 184 066 describes the manufacture of Fresnel lenses by micromachining, in which a tool of a suitable shape is used to machine a material in a particular way so as to structure it. Such a method may be relatively costly and is not suitable for mass production.
Moreover, other processes that employ photolithography methods are known. In particular it is known from U.S. Pat. No. 5,779,751 to produce, by photolithography, a stack or succession of pads of various heights, the juxtaposition of these pads eventually forming the features of the Fresnel lens.
However, methods employing photolithography processes can be relatively expensive and involve a large number of processing steps.
Other methods, especially direct structuring in a photosensitive layer, are known, for example from U.S. Pat. No. 4,609,259.
There is however a need for a relatively simple process for manufacturing segmented optical structures.
There is furthermore a need for a process enabling production of segmented optical structures with a wide variety of profiles.
The present invention aims to meet all or some of the aforementioned needs.